In today's photocopier, fax machine, printer, money machine and automatic selling machine, transmission of paper or bank notes merely takes advantage of the friction generated between the rubber roller and the paper to be fed. However, the machine's reliability is questioned. Up until the present invention, the standardization of the frictional factor was still found to be difficult, and consequently the production of a properly fitting rubber roller was difficult to achieve. Reliability seems to be obtainable only with numerous tests. As for determining the frictional factor, a spring scale capable of measuring how much force is used to pull out a paper sheet held between rubber rollers is conventionally used. The frictional factor (u) could then be calculated by dividing the measured force by the pressure exerted between rubber rollers. Although simple, the test result will be in a wide error range due to difficulty in maintaining a fixed pulling seed.